Is IO Inferior to IV Access in Out-of-Hospital Cardiac Arrest?

Is intraosseous vascular access associated with poorer patient outcomes than intravenous access after out-of-hospital cardiac arrest? In a secondary analysis, published in Annals of Emergency Medicine , researchers reviewed the encounters of 13,155 patients for nontraumatic out-of-hospital cardiac arrest (OHCA) from the Resuscitation Outcomes Consortium Prehospital Using an Impedance Valve and Early Versus Delayed (PRIMED) study.

Researchers identified whether patients had intravenous (IV) or intraosseous (IO) access. The primary outcome was favorable neurologic outcome on hospital discharge, defined as a modified Rankin score of 3 or less. Secondary outcomes were the return of spontaneous circulation and survival to hospital discharge. Researchers analyzed the data for different variables and used logistic regression to account for them, including age, sex, initial emergency medical services, shockable or nonshockable rhythm, witnessed or not-witnessed arrests, and others.

Of the encounters included in the study, 660 patients had IO access and 12,495 had IV access. Patients were separated on the basis of which route of access was initially started. They were excluded if they had any unsuccessful attempts at IO or IV access, if they had both IO and IV access, or if they had no access at all. The original PRIMED dataset excluded pregnant and incarcerated patients, those with do-not-resuscitate orders or with severe burns, and those thought to have suffered from exsanguination.

Researchers performed heavy statistical analysis on the data collected. They found that 1.5% of the final IO group and 7.6% of the final IV group had a favorable neurologic outcome. They concluded, after their multivariate regression analysis, that IO access was associated with poorer OHCA survival (odds ratio, 0.24; 95% confidence interval, 0.12-0.46).

So Where Does This Study Leave Us?

This article was interesting because it evaluates an intervention we use on a regular basis for cardiac arrest patients. Based on my experience (which I'm sure is other Medscape readers' as well), we utilize IO access whenever we cannot obtain IV access, or in certain clinical scenarios when immediate access is needed and preferable to trying unsuccessfully for IV access.

In practice, I prefer that patients get IV access, especially in critical resuscitations. Although our real-world experience probably suggests that IO access is the way to go for these situations, this study does bring up several interesting perspectives.

First, conventional or accepted wisdom may not always lend itself to easy or strong evidence when placed in a study environment. It is a good reminder that we should always keep an open mind and examine even long-held ideas about healthcare. That being said, this study also makes me wonder whether applying evidence-based medicine to all interventions makes sense. Perhaps some clinical decisions we make will not garner the expected evidence when tested.

Second, this study is a good example of something worth discussing regarding biases in research. Researchers were forthcoming with limitations for this study, including the significant difference in patient numbers between the analyzed groups. Additionally, researchers excluded patients who had both IO and IV access, or in whom either modality of access failed. This, along with other aspects of the patient selection, brings up the possibility that sicker patients or patients with characteristics that may lead to worse clinical outcomes ended up in the IO group.

Despite the conclusions of the study, in my clinical practice I will continue to utilize IO access when clinically appropriate for patients who need immediate vascular access and IV access is not possible. An IO line is typically never my endpoint for access. If necessary, once an IO has been started, as soon as it is possible, I am starting either an ultrasound-guided peripheral IV or central line, or designating another member of the resuscitation team to do so. I think we all recognize the importance of reliable vascular access. I just cannot imagine a world in which we leave the IO aside while continuously and unsuccessfully attempting IV access.

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